1. Field of the Invention
This invention generally relates to methods and systems for performing coordinate transformation, and in particular, relates to a method and system for performing coordinate transformation for navigation-guided procedures utilizing an imaging tool and a position-determining system.
2. Description of the Related Art
Navigation assistance is increasingly being used in performing medical procedures on living objects. This is typically understood to involve guidance of a medical instrument's movement relative to an area of tissue of the object to be treated. Navigation of the instrument is usually supported by means of a position-determining system. Of special interest is navigation of the instrument in areas that preclude visual monitoring by the surgeon, such as when the instrument is inserted into the interior of the patient. For this purpose, the guidance of the instrument, such as a catheter, is usually performed in a virtual 3D volume generated by means of an imaging method before or during the operation. One common method is to generate a series of 2D projections of a known geometry with the help of an X-ray diagnostic tool and to construct from these 2D images a set of 3D volume data. The set of volume data is transmitted to a navigation system, which provides a position-determining system with markers that can be detected by the system. To realize highly accurate navigation, the coordinate system of the position-determining system is typically aligned with the coordinate system of the 3D set of volume data using a process called “registration.” In one example, the registration process uses a phantom, which contains X-ray-positive markers and markers that can be detected by the position-determining system in a fixed spatial relationship relative to each other.
German Patent DE10202091A1 discloses a device and method for determining a coordinate transformation using a phantom, on which X-ray-positive markers and markers that can be detected by a position-determining system are arranged in a fixed spatial relationship relative to each other. During a scan for generating a series of 2D X-ray projections, the coordinates of the X-ray-positive markers are determined in reconstructed 3D volumes and transmitted to the position-determining system and navigation system for alignment.
German OS DE10360025A1 discloses a method of performing coordinate transformation in which markers that can be detected by a position-determining system are arranged on an imaging device, such as an X-ray radiation receiver. One of the disadvantages of this method is that when the image-capturing device is covered by a sterile cover film, the film is interposed between the markers and the position-determining system, which can be disruptive to the position-determining process. In addition, a series of markers in alignment with the device relative to the patient and the position-determining system cannot consistently be detected, which limits the accuracy of a referencing process. Moreover, the X-ray diagnostic tool cannot operate with other types of position-determining system through the markers arranged on the X-ray radiation receiver without mechanical modifications.
German Patent DE19917867B4 discloses a method and device for performing coordinate transformation for an X-ray diagnostic tool wherein a reference structure that can be detected by a position-determining system is connected detachably to the X-ray radiation receiver. After successful registration, the reference structure is removed from the X-ray radiation receiver. One of the disadvantages of this system is that when used in the application of C-arm imaging systems, the distribution of mass in the X-ray diagnostic tool is different in the area of an adjustable C-arm for the registration and diagnostic imaging processes. As such, the kinematics of the X-ray diagnostic tool in terms of the effect of the added mass on the torsion of the C-arm must be taken into account.
Accordingly, one of the objectives of the present invention is to provide an intra-operative procedure and simple and cost-effective means to determine with high accuracy the coordinate transformation between the coordinate system of the position-determining system and the coordinate system of the imaging diagnostic tool, in which the kinematics of the means necessary for image generation are described for navigation-guided procedures using an imaging diagnostic tool that can be adjusted in multiple ways and an arbitrary position-determining system of sufficient accuracy. Here, the terms “image generation” and “imaging” are also understood to include those methods that allow an image to be reconstructed from a series of measured values.